Generally, in heavy construction equipment such as an excavator, a cab door, which is opened or closed by a hinge structure, has the problem that it may be interfered with an external object, such as a surrounding building or tree, when the equipment performs a swing operation in a downtown area or in a confined place. In order to solve this problem, a sliding door device provided with a sliding door and guide rails on a cab has been known. The sliding door device enables the door to be opened or closed by guiding the sliding movement of the door on the guide rails when the door is opened or closed.
As illustrated in FIGS. 1 to 3D, a conventional sliding door device for heavy construction equipment includes a sliding door 3 sliding to move on an outer side wall 2a of a cab 2; a plurality of rails 4, 5, and 6 formed in upper, lower, and center parts of the outer side wall 2a; a plurality of rollers 7, 8, and 9 mounted on the door 3 to support the door 3 when the door 3 slides between a closed position where a doorway 2b is closed and an open position where the doorway 2b is open; a plurality of pairs of strikers 10, 11, 12, and 13, each of the pairs of strikers including a female striker 10 or 12 and a male striker 11 or 13, one of the strikers of each pair being mounted on the door 3, and the other striker of the respective pair being mounted on an outer side wall 2c, so that at least one pair of strikers are engaged with each other when the door is in its closed position and at least one pair of strikers are engaged with each other when the door is in its fully opened position; wherein at least one of the plurality of pairs of strikers 10, 11, 12, and 13 is mounted for engaging each other at a front edge portion of the door 3 when the door 3 is fully opened, and at least one other pair of the plurality of pairs of strikers is mounted for engaging each other at a rear edge portion of the door 3 when the door 3 is fully opened.
The conventional sliding door device as described above is disclosed in U.S. Pat. No. 5,577,795. An upper roller 7 includes a guide roller 7a that moves along an upper rail 4 when a door 3 is opened or closed, and a lower roller 8 includes a rolling roller 8a which is rotated in an X-axis direction (that means the front/rear direction of a cab) along the lower rail 5 to support the load of the door 3 when the door 3 is opened or closed, and a guide roller 8b which is rotated in a Y-axis direction (that means each side direction of the cab) to prevent the door 3 from seceding from the lower rail 5 when the door 3 is opened or closed (See FIG. 2).
Also, referring to FIG. 3, a center roller 9 mounted on the door 3 includes a rolling roller 9a which is rotated in an X-axis direction to support the load of the door 3 when the door 3 is opened or closed, and a guide roller 9b which is rotated in a Y-axis direction to prevent the door 3 from seceding from the center rail 6 when the door 3 is opened or closed.
As described above, in the conventional sliding door device, the female and male strikers 10 and 11 are engaged with each other in a door closed position as illustrated in FIG. 3A, while in a door open position, the female and male strikers 12, 13, 14, and 15 are engaged with each other when the door 3 is moved in the X-axis direction and approaches the rear side of the door, as illustrated in FIGS. 3B and 3D.
According to the conventional sliding door device as described above, the sliding movement of the door forms a straight or curved trace, and the load and the structure of the door or the structure of the rails may greatly hinder the opening and closing of the door. In order to improve this, continuous research and development are required.
The conventional sliding door for heavy construction equipment has the problem that the door is not kept in an open position where the sliding door is fully opened or in a closed position where the sliding door is fully closed, and secedes from the open position or the closed position due to trouble of a sliding door locking device or a door holder for fixedly keeping the open position and the closed position of the door, trouble of an upper rail or a lower rail, vibration of the equipment, and the like.
That is, according to the conventional sliding door device, due to long-term use of the door and so on, the locking state of the door is released in a fully open/closed position of the door, and the door is arbitrarily moved in front/rear direction of a cab due to the self-weight of the door even if a small vibration or impact occurs, causing the occurrence of damage of rails or rollers and safety accident.
Also, the conventional sliding door device has the problem that, in the case where the open/closed state of the door becomes unstable during working of the construction equipment, an operator in a cab should control the open/closed state of the door at any time to deteriorate the workability, and contact and interference may occur between a control lever of a working device and the body of the operator to cause the malfunction of the equipment and to reduce the manipulability.